Lances with expendable immersion sensors are typically used to measure properties of molten metals. When an immersion sensor is immersed into molten metal, measurement data, such as temperature, is communicated from the sensor device to a receiving instrument. Previously, the communication was performed using analog wiring circuits, such as those typically manufactured from copper, copper alloys or thermocouple compensating cables.
Conventional expendable molten metal immersion systems deploy devices having immersion sensors that are capable of a one-time measurement and are then discarded, as described in U.S. Pat. No. 3,643,509, the entire disclosure of which is incorporated herein by reference. Such immersion sensors are typically fixed to the distal end of a protective sleeve of the immersion device. The protective sleeve is typically manufactured from cardboard. The sensor and cardboard protective sleeve are arranged to slide fit over a hollow pipe, also known as a lance holder. The sensor is coupled to a connector member, called a contact block, as described in U.S. Pat. No. 4,893,516, the entire disclosure of which is incorporated herein by reference. The contact block is located on the pipe end and is adapted to receive the analog electrical outputs of the immersion sensor. The immersion sensor is connected to the connector member in a detachable fashion. The lance holder is internally wired with protected cables to withstand the hot environment of the pipe between the contact block and a receptacle on the end opposite of the contact block, as described in U.S. Pat. No. 5,043,023, the entire disclosure of which is incorporated herein by reference.
The receptacle provides a terminal for extending the electrical signal lines, by another analog cable, to an instrument which interprets and processes the analog signal and displays the sensor result(s). The electrical circuit, which includes the immersion sensor, the lance holder, the signal cable and the instrument, is detachably connected together by wiring and wiring connectors. Each segment of the measuring circuit, including all the electrical connections, wiring and cables are preferably constructed from materials specially compatible and compensated for the type of thermocouple or other sensor employed.
The cardboard protective sleeve of the expendable immersion sensor includes two main portions, each serving different purposes. The lower or distal portion of the protective sleeve comes in direct contact with the molten metal and is rapidly consumed in a violent reaction with the molten metal and a layer of hot slag which normally covers the molten metal surface. Sufficient mass of the cardboard sleeve is required to survive and protect the sensor at least until the sensor has completed its measurement. If the immersed cardboard sleeve prematurely fails before the measurement is obtained, in the worst case, molten metal destroys the electrical contact portion of the lance holder and the resulting damage must be repaired before another measurement can be obtained.
The second, contiguous, portion of the cardboard tube extends up and out of the molten metal bath and protects the distal end of the lance holder from metal splashing and radiant heat from the molten metal bath, slag and any close hot surface of the molten metal containment vessel. If the portion of the protective cardboard sleeve above the molten metal bath is either too short to obscure radiant heat or burns with the oxygen of the atmosphere in an acerbated fashion, the lance holder experiences localized heating. In this “hot zone”, the internal wiring of the lance holder may be subjected to extreme heat that could compromise the electrical integrity of the lance's internal wires' insulation, which could also require a repair delay before a subsequent measurement can be obtained.
During each measuring cycle, the non-disposable segments of the electrical circuit within the lance holder and those segments between the lance holder terminal and the instrument may be subject to intense radiant heat, molten metal splashing, direct contact with hot molten and other solid heated surfaces. These conditions result in insulation breakdown, tension, abrasion, and wear of the wiring, cables and connectors, leading to the eventual failure of one or more segments of the electrical circuit. The failed circuit must be repaired or replaced, resulting in additional expense and putting the necessary equipment out of operation while repairs are made. Where automated mechanical immersion systems or robots are used, repair and replacement is costly in terms of manpower, materials and the downtime of the automated system. Further, in manual immersion cases, the cable connecting the lance holder to the instrumentation is typically dragged across the floor and frequently damaged by splashing metal and mobile equipment. Such cables also present tripping hazards for workers in the immediate vicinity.
Immersion lances are not the only equipment that suffer from such problems. Sensors having internal wiring circuits are used at measuring locations in foundries and cast houses, where a portion of the metal is removed and brought to a measuring location. These sensors may suffer from failure in the analog wiring after a period of time due to the extreme conditions described above. Such sensors are described in U.S. Pat. Nos. 4,056,407, 5,037,211, 5,804,006 and 5,388,908, all of which are incorporated herein by reference.
In industrial environments of the iron and steel making industry, high temperatures are routinely encountered not only in the molten metal, but also in the surfaces and structures in and around the containers and processing vessels employed in manufacturing and transferring molten metal. Sensor devices and their corresponding measuring circuits utilized in the making, monitoring and controlling of these processes are often exposed to these harsh conditions repeatedly and with sufficient exposure to result in physical destruction and/or deterioration sufficient to render the measurements inaccurate or unavailable.
In certain industrial environments, data is transmitted acoustically within the solid material of a structure or apparatus, such as the drill casing pipe of oil rigs. Downhole telemetry devices utilizing a magnetostrictive material to generate ultrasonic waves within the metal of the drill casing are described in U.S. Pat. Nos. 5,568,448 and 5,675,325. These patents disclose the use of a magnetostrictive actuator mounted at an intermediate position in a drill pipe, wherein the drill pipe acts as a resonant tube body. An excitation current applied at a predetermined frequency to coils surrounding the magnetostrictive material of the actuator causes the drill pipe to deform. The deformation creates an acoustic or ultrasonic wave that propagates through the drill pipe material. The propagating wave signals are received by a receiver disposed uphole of the actuator and processed at the surface.
The transmission efficiency of the generated acoustic waves is best at high frequencies (generally above 400 Hz). The wave transmission drops to below acceptable levels at low frequencies (generally below 400 Hz). An acoustic telemetry system according to the above noted patents requires precise placement of the actuator and unique “tuning” of the drill pipe section with the magnetostrictive device in order to achieve the most efficient transmission, even at high frequencies. Since all drilling communication systems must resolve the ever changing length of the drill string, tuning of the acoustic devices is required. This degree of attention may be cost justified given the capital investment required for oil drilling equipment, but it is unsuited to accommodate changing lengths of mechanical immersion devices in the metal making industry.
Accordingly, it is desirable to minimize the cost of maintenance, repair and replacement of damaged molten metal measuring systems by eliminating the internal wiring thereof. It is further desirable to address the safety concerns caused by wired measuring systems used for molten metal measurements.